The damage done when corals die is even worse than scientists previously thought

When the water in the sea gets warmer, corals can get stressed, causing them to release their photosynthesising algae in a process called bleaching — so-called because the coral turns white. This is bad because the coral is then more susceptible to dying, but new research has just shown the impacts of bleaching could be worse than scientists thought.

In fact, the new research suggests that coral reefs are eroding faster than they’re growing back.

Researchers at the University of Exeter found that warmer oceans caused by last year’s strong El Niño led to a huge amount of corals dying off in the Maldives, which caused reef growth rates to collapse. Their findings were published in the journal Scientific Reports.

Coral bleaching in these areas led to extensive coral death in all the shallow water areas the team examined, and they also found species such as parrot fish have been eroding the reefs at an increased rate. The major concern is how quickly reefs recover.

Bleaching doesn’t kill corals, but it makes them vulnerable and stressed, meaning they are more likely to die. In the past, it has taken 10-15 years for corals to recover from similar situations, but the researchers explained major bleaching events may become even more frequent in a warmer world. That could be disastrous.

“It could lead to long-term loss of reef growth and so limit the coastal protection and habitat services these reefs presently provide,” Chris Perry, professor of Geography at the University of Exeter and the lead author of the study, said in a statement. “The most alarming aspect of this coral die-off event is that it has led to a rapid and very large decline in the growth rate of the reefs.”

A declining growth rate affects the ability of the reefs to match any increases in sea-level, meaning there will be less of the habitat which is critical for many marine species.

A “carbon budget” shows the balance between how quickly coral reefs are growing and the rate at which the reefs are removed by erosion. It’s called this because it measures the uptake and emission of carbon dioxide of the system. Photosynthetic algae in the coral absorb carbon dioxide, but the reef can also release it.

Using this measurement, the team found that, despite some natural growth, the reefs had still reduced overall — by 157%, in fact, on average. In other words, they’re disappearing more quickly than they’re reappearing.

Why are coral reefs important?

Coral reefs are built up over hundreds to thousands of years, accumulating into the structures that support a huge diversity of life, such as fish, crabs, and shrimp. They are made up of coral skeletons, which are formed from calcium carbonate, and they provide numerous benefits.

“They are vital habitats, essential for a vast number of species and they are also important for tourism and food provision,” said Dr Kyle Morgan in a statement.

But it’s taking a long time for the reefs to come back from warmer temperatures.

“Based on past trajectories, we predict recovery will take at least a decade, however it all depends on the extent of future warming events and climate change,” added Morgan.